The present invention relates to digital manufacturing (DM) systems, such as rapid prototyping and rapid manufacturing systems, that use various methods, such as fused deposition modeling, stereo-lithography, selective laser sintering, and similar techniques, for building three-dimensional (3D) objects. In particular, the present invention relates to extrusion based layered deposition systems for producing multiple, identical objects.
An extrusion based layered deposition system deposits a flowable build material to build a 3D solid object from a computer-aided design (CAD) model, typically in a rapid prototyping or manufacturing setting. Various such systems are described in U.S. Pat. Nos. 5,968,561 to Batchelder et al., 6,722,872 to Swanson et al. and 7,314,591 to Priedeman, Jr., all of which are assigned to Stratasys, Inc., Eden Prairie, Minn. The build material is heated and extruded through a first extrusion nozzle carried by an extrusion head, and is deposited in a layer-by-layer manner as a sequence of roads on a substrate in a planar (X, Y) surface. The extruded build material fuses to previously deposited build material, and solidifies upon a decrease in temperature. The position of the extrusion head relative to the substrate is then incremented perpendicularly to the planar surface in a Z-direction, and the process is repeated to form a 3D object resembling the CAD model.
In fabricating 3D objects by depositing layers of build material atop previously deposited build material, it is often necessary to fabricate a support for layers of build material larger than the previously deposited layers, which are not supported by the build material itself. Typically, a second extrusion nozzle deposits layers of a support material to build up a support utilizing a deposition process similar to that used for depositing the build material. The support material is formulated to adhere to the build material during deposition, and to easily separate from the solidified build material after the build process is completed. In order to prevent interference of the inactive extrusion nozzle with the active extrusion process, the second extrusion nozzle is often movable in the Z-direction relative to first extrusion nozzle. It is necessary to calibrate movement of the second extrusion nozzle such that its position when active is known and the position of the substrate can be properly adjusted in the Z-direction. Typically, the calibration is conducted manually by shimming the second extrusion nozzle after running the extrusion head through a series of test patterns. Such a method is, however, time consuming and not repeatable, but produces movement of the second extrusion nozzle within an acceptable tolerance limit for production of a single 3D object.
Movement of the extrusion head within the (X, Y) plane relative to the substrate, movement of the substrate in the Z-direction relative to the extrusion head, and movement of the extrusion nozzles in the Z-direction relative to each other are coordinated through a computer that manipulates drive systems for the extrusion head. The computer converts data representing the CAD model into build data that determines when to activate the build and support extrusion nozzles. The build data is obtained by dividing the CAD model of the 3D object into multiple horizontally sliced layers and determining the location of support structures. Then, for each sliced layer, the computer generates a build path for depositing roads of build material and support material on the substrate to form the 3D object and corresponding supports. As such, a single extrusion based layered deposition system is capable of rapidly producing a single 3D object with build data generated from a CAD model through carefully orchestrated movements of the extrusion head, substrate and extruders.
In order to produce multiple 3D objects that are identical, it is conventionally required to run the deposition process multiple times using the same build data. Thus, throughput of a single deposition system is limited by the length of each deposition process. In order to increase throughput, multiple extrusion based layered deposition systems can be employed, each operating with the same build data. In addition to high costs, such multi-machine deposition systems require large amounts of floor space and redundant components. Conversely, when only a single prototype object is needed, multiple deposition system machines lay idle while a single machine produces the object. Various DM systems include multiple means for forming extrusion material in order to more rapidly produce a single object. For example, U.S. Pat. No. 6,406,658 to Manners et al, which is assigned to 3D Systems, Inc., Valencia, Calif., describes a stereo-lithography system having a dual spot scanner for solidifying material for a single object. Likewise, U.S. Pat. No. 7,077,638 to Leyden et al, also assigned to 3D Systems, Inc., describes a 3D modeling system using a multi-orifice head for dispensing a single material for building and supporting a single object. There is, however, a need for further increasing throughput of DM systems, particularly extrusion based layered deposition systems.